chemicals in the environment that might play a role in parkinson's disease. >> narrator: the findings galvanized the scientific community. researchers began looking into whether parkinson's was caused by a variety of environmental triggers, and history seemed to support that approach. scientists knew that parkinson's hadn't even appeared in the medical literature until 1817, the beginning of the industrial revolution, when toxins were first poured into the environment. they now wondered if parkinson's could be, at least in part, a modern disease, triggered by toxins like mptp. >> i think it's a very exciting time for research in this disease. and for patients with parkinson's disease, and their families, that's good news. thank you very much. we had real hope that this would solve the disease. and i thought, three to four years we would have the answer. in fact, in three to four years, we did have an answer, and that was that mptp itself was not the cause of parkinson's. >> narrator: not the cause, but a key clue. indeed, recent studies have built on langston's initial breakthrough, s